* Paul E. McKenney ([email protected]) wrote: > On Mon, Sep 03, 2012 at 02:03:00PM -0400, Mathieu Desnoyers wrote: > > * Paul E. McKenney ([email protected]) wrote: > > > This commit ensures that all read-side functions meet the 10-line LGPL > > > criterion that permits them to be expanded directly into non-LGPL code, > > > without function-call instructions. It also documents this as the intent. > > > > > > Signed-off-by: Paul E. McKenney <[email protected]> > > > > > > diff --git a/urcu/static/urcu-bp.h b/urcu/static/urcu-bp.h > > > index e7b2eda..881b4a4 100644 > > > --- a/urcu/static/urcu-bp.h > > > +++ b/urcu/static/urcu-bp.h > > > @@ -6,8 +6,8 @@ > > > * > > > * Userspace RCU header. > > > * > > > - * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking > > > - * dynamically with the userspace rcu library. > > > + * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU > > > + * RELEASE. See urcu.h for linking dynamically with the userspace rcu > > > library. > > > * > > > * Copyright (c) 2009 Mathieu Desnoyers <[email protected]> > > > * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. > > > @@ -162,32 +162,48 @@ static inline int rcu_old_gp_ongoing(long *value) > > > ((v ^ rcu_gp_ctr) & RCU_GP_CTR_PHASE); > > > } > > > > > > +/* > > > + * Helper for _rcu_read_lock(). The format of rcu_gp_ctr (as well as > > > + * the per-thread rcu_reader.ctr) has the upper bits containing a count > > > of > > > + * _rcu_read_lock() nesting, and a lower-order bit that contains either > > > zero > > > + * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in > > > + * _rcu_read_lock() happen before the subsequent read-side critical > > > section. > > > + */ > > > +static inline void _rcu_read_lock_help(unsigned long tmp) > > > > could we rename the "_rcu_read_lock_help" to "_rcu_read_lock_update" ? > > > > I think it would fit better the role of this function in the algorithm. > > > > As Josh pointed out, "directloy" -> "directly" below, > > > > The rest looks good. I'll wait for an updated version. > > Here you go!
Merged as: commit a5a9f428a238e790d6c97299bc214b5cca815cd7 Author: Paul E. McKenney <[email protected]> Date: Thu Sep 6 21:15:53 2012 -0400 Ensure that read-side functions meet 10-line LGPL criterion This commit ensures that all read-side functions meet the 10-line LGPL criterion that permits them to be expanded directly into non-LGPL code, without function-call instructions. It also documents this as the intent. [ paulmck: Spelling fixes called out by Josh Triplett and name change called out by Mathieu Desnoyers (_rcu_read_lock_help() -> _rcu_read_lock_update(). ] [ Mathieu Desnoyers: _rcu_read_unlock_help renamed to _rcu_read_unlock_update_and_wakeup, and spelling fix for preced -> precede. ] Signed-off-by: Paul E. McKenney <[email protected]> Signed-off-by: Mathieu Desnoyers <[email protected]> Thanks! Now we should possibly find another #define than _LGPL_SOURCE to let non-lgpl code specify that they want to use the inline versions ? E.g. _URCU_INLINE maybe ? Thanks, Mathieu > > Thanx, Paul > > ------------------------------------------------------------------------ > > Ensure that read-side functions meet 10-line LGPL criterion > > This commit ensures that all read-side functions meet the 10-line LGPL > criterion that permits them to be expanded directly into non-LGPL code, > without function-call instructions. It also documents this as the intent. > > [ paulmck: Spelling fixes called out by Josh Triplett and name > change called out by Mathieu Desnoyers (_rcu_read_lock_help() -> > _rcu_read_lock_update(). ] > > Signed-off-by: Paul E. McKenney <[email protected]> > > diff --git a/urcu/static/urcu-bp.h b/urcu/static/urcu-bp.h > index e7b2eda..a2f7368 100644 > --- a/urcu/static/urcu-bp.h > +++ b/urcu/static/urcu-bp.h > @@ -6,8 +6,8 @@ > * > * Userspace RCU header. > * > - * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking > - * dynamically with the userspace rcu library. > + * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU > + * RELEASE. See urcu.h for linking dynamically with the userspace rcu > library. > * > * Copyright (c) 2009 Mathieu Desnoyers <[email protected]> > * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. > @@ -162,32 +162,48 @@ static inline int rcu_old_gp_ongoing(long *value) > ((v ^ rcu_gp_ctr) & RCU_GP_CTR_PHASE); > } > > +/* > + * Helper for _rcu_read_lock(). The format of rcu_gp_ctr (as well as > + * the per-thread rcu_reader.ctr) has the upper bits containing a count of > + * _rcu_read_lock() nesting, and a lower-order bit that contains either zero > + * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in > + * _rcu_read_lock() happen before the subsequent read-side critical section. > + */ > +static inline void _rcu_read_lock_update(unsigned long tmp) > +{ > + if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) { > + _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, > _CMM_LOAD_SHARED(rcu_gp_ctr)); > + cmm_smp_mb(); > + } else > + _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, tmp + > RCU_GP_COUNT); > +} > + > +/* > + * Enter an RCU read-side critical section. > + * > + * The first cmm_barrier() call ensures that the compiler does not reorder > + * the body of _rcu_read_lock() with a mutex. > + * > + * This function and its helper are both less than 10 lines long. The > + * intent is that this function meets the 10-line criterion in LGPL, > + * allowing this function to be invoked directly from non-LGPL code. > + */ > static inline void _rcu_read_lock(void) > { > long tmp; > > - /* Check if registered */ > if (caa_unlikely(!URCU_TLS(rcu_reader))) > - rcu_bp_register(); > - > + rcu_bp_register(); /* If not yet registered. */ > cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ > tmp = URCU_TLS(rcu_reader)->ctr; > - /* > - * rcu_gp_ctr is > - * RCU_GP_COUNT | (~RCU_GP_CTR_PHASE or RCU_GP_CTR_PHASE) > - */ > - if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) { > - _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, > _CMM_LOAD_SHARED(rcu_gp_ctr)); > - /* > - * Set active readers count for outermost nesting level before > - * accessing the pointer. > - */ > - cmm_smp_mb(); > - } else { > - _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, tmp + > RCU_GP_COUNT); > - } > + _rcu_read_lock_update(tmp); > } > > +/* > + * Exit an RCU read-side critical section. This function is less than > + * 10 lines of code, and is intended to be usable by non-LGPL code, as > + * called out in LGPL. > + */ > static inline void _rcu_read_unlock(void) > { > /* > diff --git a/urcu/static/urcu-pointer.h b/urcu/static/urcu-pointer.h > index 48dc5bf..4361156 100644 > --- a/urcu/static/urcu-pointer.h > +++ b/urcu/static/urcu-pointer.h > @@ -6,8 +6,8 @@ > * > * Userspace RCU header. Operations on pointers. > * > - * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-pointer.h for > - * linking dynamically with the userspace rcu library. > + * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU > + * RELEASE. See urcu.h for linking dynamically with the userspace rcu > library. > * > * Copyright (c) 2009 Mathieu Desnoyers <[email protected]> > * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. > @@ -59,8 +59,11 @@ extern "C" { > * addition to forthcoming C++ standard. > * > * Should match rcu_assign_pointer() or rcu_xchg_pointer(). > + * > + * This macro is less than 10 lines long. The intent is that this macro > + * meets the 10-line criterion in LGPL, allowing this function to be > + * expanded directly in non-LGPL code. > */ > - > #define _rcu_dereference(p) ({ \ > __typeof__(p) _________p1 = CMM_LOAD_SHARED(p); > \ > cmm_smp_read_barrier_depends(); \ > @@ -73,8 +76,11 @@ extern "C" { > * data structure, which can be safely freed after waiting for a quiescent > state > * using synchronize_rcu(). If fails (unexpected value), returns old (which > * should not be freed !). > + * > + * This macro is less than 10 lines long. The intent is that this macro > + * meets the 10-line criterion in LGPL, allowing this function to be > + * expanded directly in non-LGPL code. > */ > - > #define _rcu_cmpxchg_pointer(p, old, _new) \ > ({ \ > __typeof__(*p) _________pold = (old); \ > @@ -89,8 +95,11 @@ extern "C" { > * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous > * pointer to the data structure, which can be safely freed after waiting > for a > * quiescent state using synchronize_rcu(). > + * > + * This macro is less than 10 lines long. The intent is that this macro > + * meets the 10-line criterion in LGPL, allowing this function to be > + * expanded directly in non-LGPL code. > */ > - > #define _rcu_xchg_pointer(p, v) \ > ({ \ > __typeof__(*p) _________pv = (v); \ > @@ -121,8 +130,11 @@ extern "C" { > * data structure before its publication. > * > * Should match rcu_dereference_pointer(). > + * > + * This macro is less than 10 lines long. The intent is that this macro > + * meets the 10-line criterion in LGPL, allowing this function to be > + * expanded directly in non-LGPL code. > */ > - > #define _rcu_assign_pointer(p, v) _rcu_set_pointer(&(p), v) > > #ifdef __cplusplus > diff --git a/urcu/static/urcu-qsbr.h b/urcu/static/urcu-qsbr.h > index 22908a4..5580092 100644 > --- a/urcu/static/urcu-qsbr.h > +++ b/urcu/static/urcu-qsbr.h > @@ -6,8 +6,8 @@ > * > * Userspace RCU QSBR header. > * > - * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-qsbr.h for linking > - * dynamically with the userspace rcu QSBR library. > + * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU > + * RELEASE. See urcu.h for linking dynamically with the userspace rcu > library. > * > * Copyright (c) 2009 Mathieu Desnoyers <[email protected]> > * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. > @@ -157,15 +157,36 @@ static inline int rcu_gp_ongoing(unsigned long *ctr) > return v && (v != rcu_gp_ctr); > } > > +/* > + * Enter an RCU read-side critical section. > + * > + * This function is less than 10 lines long. The intent is that this > + * function meets the 10-line criterion for LGPL, allowing this function > + * to be invoked directly from non-LGPL code. > + */ > static inline void _rcu_read_lock(void) > { > rcu_assert(URCU_TLS(rcu_reader).ctr); > } > > +/* > + * Exit an RCU read-side critical section. > + * > + * This function is less than 10 lines long. The intent is that this > + * function meets the 10-line criterion for LGPL, allowing this function > + * to be invoked directly from non-LGPL code. > + */ > static inline void _rcu_read_unlock(void) > { > } > > +/* > + * Inform RCU of a quiescent state. > + * > + * This function is less than 10 lines long. The intent is that this > + * function meets the 10-line criterion for LGPL, allowing this function > + * to be invoked directly from non-LGPL code. > + */ > static inline void _rcu_quiescent_state(void) > { > cmm_smp_mb(); > @@ -175,6 +196,14 @@ static inline void _rcu_quiescent_state(void) > cmm_smp_mb(); > } > > +/* > + * Take a thread offline, prohibiting it from entering further RCU > + * read-side critical sections. > + * > + * This function is less than 10 lines long. The intent is that this > + * function meets the 10-line criterion for LGPL, allowing this function > + * to be invoked directly from non-LGPL code. > + */ > static inline void _rcu_thread_offline(void) > { > cmm_smp_mb(); > @@ -184,6 +213,14 @@ static inline void _rcu_thread_offline(void) > cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ > } > > +/* > + * Bring a thread online, allowing it to once again enter RCU > + * read-side critical sections. > + * > + * This function is less than 10 lines long. The intent is that this > + * function meets the 10-line criterion for LGPL, allowing this function > + * to be invoked directly from non-LGPL code. > + */ > static inline void _rcu_thread_online(void) > { > cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ > diff --git a/urcu/static/urcu.h b/urcu/static/urcu.h > index f27f8b6..f211dab 100644 > --- a/urcu/static/urcu.h > +++ b/urcu/static/urcu.h > @@ -6,8 +6,8 @@ > * > * Userspace RCU header. > * > - * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking > - * dynamically with the userspace rcu library. > + * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU > + * RELEASE. See urcu.h for linking dynamically with the userspace rcu > library. > * > * Copyright (c) 2009 Mathieu Desnoyers <[email protected]> > * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. > @@ -252,46 +252,71 @@ static inline int rcu_gp_ongoing(unsigned long *ctr) > ((v ^ rcu_gp_ctr) & RCU_GP_CTR_PHASE); > } > > -static inline void _rcu_read_lock(void) > +/* > + * Helper for _rcu_read_lock(). The format of rcu_gp_ctr (as well as > + * the per-thread rcu_reader.ctr) has the upper bits containing a count of > + * _rcu_read_lock() nesting, and a lower-order bit that contains either zero > + * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in > + * _rcu_read_lock() happen before the subsequent read-side critical section. > + */ > +static inline void _rcu_read_lock_update(unsigned long tmp) > { > - unsigned long tmp; > - > - cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ > - tmp = URCU_TLS(rcu_reader).ctr; > - /* > - * rcu_gp_ctr is > - * RCU_GP_COUNT | (~RCU_GP_CTR_PHASE or RCU_GP_CTR_PHASE) > - */ > if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) { > _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, > _CMM_LOAD_SHARED(rcu_gp_ctr)); > - /* > - * Set active readers count for outermost nesting level before > - * accessing the pointer. See smp_mb_master(). > - */ > smp_mb_slave(RCU_MB_GROUP); > - } else { > + } else > _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, tmp + RCU_GP_COUNT); > - } > } > > -static inline void _rcu_read_unlock(void) > +/* > + * Enter an RCU read-side critical section. > + * > + * The first cmm_barrier() call ensures that the compiler does not reorder > + * the body of _rcu_read_lock() with a mutex. > + * > + * This function and its helper are both less than 10 lines long. The > + * intent is that this function meets the 10-line criterion in LGPL, > + * allowing this function to be invoked directly from non-LGPL code. > + */ > +static inline void _rcu_read_lock(void) > { > unsigned long tmp; > > + cmm_barrier(); > tmp = URCU_TLS(rcu_reader).ctr; > - /* > - * Finish using rcu before decrementing the pointer. > - * See smp_mb_master(). > - */ > + _rcu_read_lock_update(tmp); > +} > + > +/* > + * This is a helper function for _rcu_read_unlock(). > + * > + * The first smp_mb_slave() call ensures that the critical section is > + * seen to preced the store to rcu_reader.ctr. > + * The second smp_mb_slave() call ensures that we write to rcu_reader.ctr > + * before reading the update-side futex. > + */ > +static inline void _rcu_read_unlock_help(unsigned long tmp) > +{ > if (caa_likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) { > smp_mb_slave(RCU_MB_GROUP); > _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, > URCU_TLS(rcu_reader).ctr - RCU_GP_COUNT); > - /* write URCU_TLS(rcu_reader).ctr before read futex */ > smp_mb_slave(RCU_MB_GROUP); > wake_up_gp(); > - } else { > + } else > _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, > URCU_TLS(rcu_reader).ctr - RCU_GP_COUNT); > - } > +} > + > +/* > + * Exit an RCU read-side crtical section. Both this function and its > + * helper are smaller than 10 lines of code, and are intended to be > + * usable by non-LGPL code, as called out in LGPL. > + */ > +static inline void _rcu_read_unlock(void) > +{ > + unsigned long tmp; > + > + tmp = URCU_TLS(rcu_reader).ctr; > + _rcu_read_unlock_help(tmp); > cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */ > } > > -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com _______________________________________________ lttng-dev mailing list [email protected] http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
